#include<stdio.h>
#include<stdlib.h>
int main(int argc,char*argv[]){
    if(argc<3)return 1;
    int n=atoi(argv[1]);
    if(n<1||n>10)return 0;
    int total_sum=n*(n+1)/2;
    long long input_sum=0;
    int element_count=0;
    
    for(int i=2;i<argc;i++){
        int element=atoi(argv[i]);
         if(element<=0){
             printf("Invalid Input");
             return 0;
         }
    
    input_sum+=element;
    element_count++;
   }
   if(element_count!=n-1)return 0;
   printf("%d\n",total_sum(int)input_sum);
   return 0;

}